AUTO-TRACKING Operaton

Remote Sensing. To remote sense with auto-series operation, set SENSE switch of the master unit and set SENSE switch of the slave unit to remote.

Remote Analog Voltage Programming. To remote analog pro- gram with auto-series operation, connect program (external) volt- ages to the "CV" or "CC"" terminal of the master unit and set "CV" or "CC" switch of the master unit to remote.

Auto-tracking operation of power supplies is similar to auto-series operation except that the master and slave supplies have the same output polarity with respect to a common bus or ground. This operation is useful where simultaneous turn-up, turn-down or proportional control of all power supplies is required.

Figure 14 and Figure 15 show two and three supplies connected in auto-tracking with their negative output terminals connected together as a common or ground point. For two units in auto- tracking a fraction R2/(R1+R2) of the output of the master supply is provided as one of the inputs to the comparison amplifier of the slave supply, thus controlling the slave's output. The master sup- ply in an auto-tracking operation must be the positive supply hav- ing the largest output voltage. Turn-up and turn-down of the power supplies are controlled by the master supply. In order to maintain the temperature coefficient and stability specifications of the power supply, the external resistor should be stable, low noise, low temperature.

Determining Resistors. External resistors control the fraction of the master unit's voltage that is supplied from the slave unit. For two units in auto-tracking the ratio R1 and R2 is

R2/(R1+R2	= (Vs/Vm)
Where Vm	= master output voltage
Vs	= slave output voltage

It is recommended to connect a 0.1 μF capacitor in paral- lel with R2 in two supplies operation or R2 and R4 in three supplies operation to ensure the stable operation.

Setting Voltage and Current. Use the master unit's VOLTAGE con- trol to set the output voltage from both units. When the master is in CV operation, the master's output voltage(Vm) is the same as its voltage setting, and the slave's output voltage for two units operation is Vm(R2/(R1+R2)). The VOLTAGE control of the slave unit is dis- abled. Set the CURRENT controls of master and slave units above the required currents to assure CV operation of master and slave units.

Overvoltage Protection. Set the OVP shutdown voltage in each unit so that it shuts down at a voltage higher than its output volt- age during auto-tracking operation. When a master unit shuts down, it programs any slave units to zero output. When a slave unit shuts down, it shuts down only itself.

Remote Sensing. To include remote sensing with auto-tracking operation independently, set up each unit for remote sensing according to the remote-sensing instructions under previous paragraph.

Remote Analog Programming. To simultaneously remote pro- gram both units' output voltages, set up only the master unit for remote voltage programming according to the remote program- ming instructions. To vary the fraction of the output voltage contri- bution by the slave unit, connect a variable resistor in place of R2 in two units operation. To independently remote program each unit's output current setting, set up each unit for remote control of output current according to the instructions under "Remote Pro- gramming, Constant Current" paragraph.

MASTER POWER SUPPLY

MASTER

LOCAL

M/S 1

M/S 2

SENSE

OUT

-S

VREF A1 A2

A4 A5

SLAVE

REMOTE

LOAD

SLAVE POWER SUPPLY

MASTER

LOCAL

M/S 1

M/S 2

SENSE

OUT

-S

VREF A1 A2

A4 A5

SLAVE

REMOTE

Figure 14. Auto-Tracking Operation of Two Supplies

MASTER POWER SUPPLY

+ _

MASTER

LOCAL

M/S 1

M/S 2

SENSE

OUT

-S

CC VREF A1 A2

SLAVE

REMOTE

LOAD

SLAVE POWER SUPPLY(S1)

+ _

MASTER

LOCAL

M/S 1

M/S 2

SENSE

OUT

-S

CC VREF A1 A2

SLAVE

REMOTE

LOAD

SLAVE POWER SUPPLY(S2)

+ _

MASTER

LOCAL

M/S 1

M/S 2

SENSE

OUT

-S

CC VREF A1 A2

SLAVE

REMOTE

Where

Vm = masters unit's output voltage

Vs1 = R1+ R2

Vs1 = slave(S1) unit's output voltage

Vs2 =

Vs1

Vs2 = slave(S2) unit's output voltage

R3+ R4

Figure 15. Auto-Tracking Operation of Three Supplies

1-13